They say clematis like their feet in the shade and their shoulders in the sun. If that is the case, then H.F. Young is in exactly the right spot. The other two - not so much. Those vines get around two to three hours of sun in the afternoon, and that's about it. Maybe that explains why H.F. Young took off so quickly, while the other two were very slow to develop.
Either way, I'm happy with the placement of these vines, and I'm happy that Henryi and Franziska Marie have finally grown so large.